NISHISHIBA/Electric Propulsion System
An electric propulsion system, which has realized a low-vibration and low-noise environment together with high maneuverability and reliability, is the most effective system for safe navigation and living comfort on board, Furthermore, electric propulsion makes engine-room compact because it does not necessitate the concentration of propulsion-related equipment in the engine room. Based on various state-of-the-art systems, including Transistor (IGBT) inverters, Thyristor motors, GTO inverters and cycle-converters, which have made remarkable progress in recent years, Nishishiba's electric propulsion system offers an optimum option.
Recently, a thyristor motor electric propulsion system comprising two motors to drive twin propellers was delivered for installation in the large oceanographic research vessel "Mirai." This system is taken up in this article to illustrate Nishishiba's achievements in this field.
Specifications
◆ Rated output：
700kW x 2
◆ Operating range：
90min-1〜20min-1, -75min-1〜-20min-1
◆ 2 sets-Propulsion synchronous motor
12 Poles, 440V, 3 Phase, 0.75PF, F-Insu.class, brushless, totally enclosed water cooled air cooler and fans, special winding for 12 pulse control
◆ 2 sets-Propulsion control panel：
12 pulse thyristor motor system
Self check function
-Check of stand-by condition
-Reference of sequential alarm
-Display of inspection items at fault condition
◆ 2 sets-Transformer
3 phase, 1500kVA, 450V/450V-450V (△-Y/△), dry type, H-Insu. class and forced ventilation
The vessel, using a hybrid diesel-electric propulsion system, mainly runs on two 700 kW electric motors during oceanographic observation.
Features of this electric propulsion system are outlined below.
1. Twelve-pulse control
Twelve-pulse control is used to restrain vibration during navigation and reduce the effect of harmonics on the power source.
Each motor is provided with two sets of armature coils, whose phase angles are electrically shifted by 30 degrees, and the torque pulsation of each coil overlaps that of the other with a 30-degree phase difference reduces the amplitude of fluctuation. The power source is connected to the inverter via a triple-coil transformer configured in a connection form of △-Y/△, so that the 5th, 7th, 17th, 19th and etc., harmonic components cancel one another vectorially to reduce harmonic components on the power source side.
2. Regenerative braking control
For emergency stopping in a crash astern or crash ahead motion, regenerating braking control is built in.
In order to minimize the effect on the frequency of the bus line, the start-up regenerative current is subjected to sloped control.
3. Control of synchronized operation of propellers
To reduce vibrations generated by the twin propellers in the hull right above them, the phase angles of the twin propellers are set at given angles for synchronized operations at a set phase angle.
4. Operation support system
To facilitate monitoring, maintenance and inspection, a monitor panel on the control board offers the ability to graphically display the operating state of the system, to check the adjuster and to conduct self-diagnosis.
Nishishiba Electric Co., Ltd.
Address; Nissei Shiba Bldg., 6-10, Shiba 1-chome, Minato-ku, Tokyo 105-0014
Tel： +81-3-3454-6411 Fax： +81-3-3454-6430
